1. Field of the Invention
This invention relates to the recovery of the heat transfer in heat exchangers in circulation loops in which drag-reducing surfactant solutions are used for reduction of pumping power expended to pump heat exchanging fluid through the hydronic system.
2. Description of the Prior Art
Drag-reducing additives can decrease friction in pipes with all else being equal. This reduced pipe wall friction does result in a decrease in the pumping power necessary to circulate a fluid in a piping system, or alternatively could result in greater flow rate or even in longer system reach than without additives. A decrease in pumping power would save energy in many systems such as recirculating hydronic HVAC systems or other types where water or another fluid are used as thermal transport agent for cooling or heating.
Unfortunately, if the system includes heat exchangers, the heat transfer is also greatly decreased by the additives and the heat exchangers show reduced efficiency. In the case of a cooling system, for example, the chiller has to work with larger refrigerant temperature difference, and the energy savings in the pumps are countered by the additional chiller work, and the total energy savings may be reduced, eliminated, or there could even be a net increase in overall system energy use. A similar effect is seen in heating systems. By introducing a conventional heat transfer enhancement device it is possible to modify the flow and to increase heat transfer as in the case of water, but this is generally not a suitable solution because the losses due to the insert are too high in many cases.
Drag-reducing surfactant solutions have been used for reducing pumping power in circulation systems under turbulent flow conditions. The reduced heat transfer that inevitably accompanies drag reduction in any turbulent pipe flow was accepted as an undesirable by-effect in most applications or uses. Special types of heat exchangers, like plate heat exchangers, which make use of narrow passages instead of pipes, show smaller heat and drag reductions. In general, however, the application of drag-reducing additives in any circulation system that includes heat transfer in most possible applications is inhibited by reduction of heat transfer efficiency in the heat exchangers.
What is needed is an apparatus and method whereby the use of any type of heat exchanger with drag-reducing surfactant additives can be realized without substantial or excessive reduction in heat transfer.